Torque measuring device for shafts



Feb. 21, 1950 B. F. LANGER 2,498,282

TORQUE MEASURING DEVICE FOR SHAFTS Original Filed Sept. 15, 1942 2 shees-sneet 1 25 WITNESSES: 19G 25f 35b 17a W MJWLJ-JA 4/ f firhardi l 01798). W

ATTORNEY Feb. 21, 1950 B. F. LANGER 2,498,282

TORQUE MEASURING DEVICE FOR SHAFTS Original Filed Sept. 15, 1942 2 Sheets-Sheet 2 El Z a! Q 251 e INVENTOR Bernard 1? La); en 53% BY 9" We? 7 f4? ATTORNEY rotating member.

speed applications.

Patented F eb. 21, 1950 TORQUE MEASURING DEVICE FOR SHAFTS Bernard F. Langer, Pittsburgh, Pa., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Original application September 15, 1942, Serial No. 458,378. Divided and this application May 15, 1946, Serial No. 669,801

7 Claims. 1

This application is a division. of the copending application, Serial No. 458,378, filed September 1:5, 1942, entitled Torque measuring devices for shafts and assigned to the same assignee as this invention. The copending application is now United. States Patent 2,459,171 which issued on January 18, 1949.

The present invention relates to torque indicating or measuring devices such as those operable in response to the elastic deformations of a shaft.

More particularly, the present invention relates to a novel electromagnetic device operable in response. to the torque characteristics of a shaft transmitting power.

Numerous efforts have been made in the past to providesuitable devices for indicating or measuring the power transmitted by a rotating shaft without using the conventional dynamometer methods. They have consisted in part of the attachment of magnetic strain gauges, optical systems and the attachment of variable capacity electrical. condensers on the shaft. Most of these .devices operate in the manner of torque meters, which measure.- the' torsionalv or circumferential distortions of a known gauge length. of the shaft transmitting power which accurately reflects the torque being. transmitted by the given shaft.

, Most of the above schemes require the attachment of electrical connections to the shaft element by means such as slip rings on the shaft and brushes for picking up the current. l-Ioweven. due to the electrical. characteristics of the slip ring and brush assembly, when the quantity to be measured is: small, large errors are introduced into the metering system thus providing highly unsatisfactory indications of the desired .shaft. condition.

Another important disadvantage of other systerm is that they require the use of mechanically delicate elements such as electric coils on the This is undesirable inhigh In the present device: the rotating parts are all extremely rugged.

Efforts directed to overcoming these undesirable conditions have; led to the development of the inductor generator type of measuring devices. In thistypeof devicetwoinductor generators are displaced from each. other. along. a shaft system: and arev so connected and arranged that their outputv voltages are equal and opposed in phase relation to each other when theshaft. is rotating without load- Whenv a. load is connected to therotating shaft, the shaft. undergoes torsional. deflection, that is, the shaft twists, and the phase relation of. the one generator relative to 2 the other is shifted such that a voltage difference will appear between the generated voltages indicative of the power being transmitted by the shaft. This condition obtains, however, only through a limited range of phase shift.

While this type of indicator is relatively simple and for some applications provides a ready means for measuring shaft horsepower, it has the disadvantage of requiring a relatively long gauge length of shaft. Further it is difficult to construct a generatorof this type which is free from the error introducing effects of shaft bending, temperature, end thrust and calibration errors due to variations in the magnetizing source. Indications are that phase shifts of 5 to 10 electrical degrees will provide quite reliable operation, but such phase shifts are available only on long gauge lengths of shafts; the usual available phase shift being of the order of a fraction of an electrical degree. Another disadvantage lies in the fact that in order to indicate torque the speed effect must be eliminated from the generated voltages.

A further characteristic which may sometimes be undesirable is the fact that the device cannot be calibrated statically, by that is meant, th-at the shaft must be rotating in order that voltage may be generated.

A principal. object of the present invention is to provide a torque measuring device that will respond to the torque characteristics of a shaft and produce an electrical current or voltage accurately indicative of the aforenamed characteristic.

Another object of the present invention is to providea torque measuring device that will eliminate the use of slip rings and brushes.

Another object of the present invention is to provide a torque measuring device of such mechanical design as to be self compensating for relative changes of positions of the component parts due to temperature, end thrust of the shaft and bendingof the shaft the torque loading: of which. is to be measured.

Another object of the present invention is to provide a torque measuring device that will respond to the slight circumferential or torsional distortions, that is, twist, of small gauge length of shafts.

A further object of the present invention is to provide a torque measuring device of compact construction that will be adaptable for use in relatively small spaces.

.A specific object of the: present invention is to 3 provide a torque measuring device that may be calibrated statically.

A further specific object of the present invention is to provide a measuring device of balanced construction that it may operate at high speeds withoutlintroducing vibrations into the given shaft or shaft system.

A still further specific object of the present invention is to provide a torque measuring device adaptable for use on large diameter shafts as, for example, marine propeller shafts.

Other objects and advantages will become more apparent from a study of the following specification when considered in conjunction with the accompanying drawings, in which:

Figure l is a view partially in section of a torque measuring device embodying the fundamental principles of this invention.

Fig. 2 is a sectional view taken on the line' IIII of Fi 1.

Fig. 3 is a view partially in section of a modification of this invention.

Fig. 4 is a sectional view taken on the line IV- IV of Fi 3.

Fig. 5 is a view partially in section showing a modified form of the invention illustrated in Fig. '3.

Fig. 6 is a sectional view taken on the line VI- VI of Fig. 5.

Fig. 7 is a View in full section illustrating a reversed or inside out construction of the invention illustrated in .Fig. 5.

Fig. 8 is a sectional view taken on the line VIII-VIII of Fig. 7.

Fig. 9 is a view, partially in section, illustrating a modification of this invention as applied to large diameter shafts such as marine propeller shafts.

Fig. 10 is a sectional view taken on the line XX of Fig. 9.

Fig. 11 is a sectional view of a portion of a further modification of this invention.

Fig. 12 is a partial view showing a modification of the invention illustrated in Fig. 10.

In many cases it is'desirable to have a contin- 'uous'indication of the power output of a prime mover. This conditionis particularly true in the marine and aviation fields. In operating airmeans for indicating in terms of torque and speed the power output of an engine provides means for readily obtaining the desired rate of fuel consumption.

The torque load of such an engine is accurately indicated by the elastic torque characteristic of the drive shaft or shaft system connected therei to, the torque characteristic in this case being the circumferential or torsional deflection of a known gauge length of shaft. With the apparatus disclosed in this specification, it is possible to utilize :this torque characteristic to obtain an electrical measurement of the torque loading of the shaft.

A power measuring device of the type utilizing the torsional characteristic and speed of rotation of a shaft is disclosed in the copending application of F.W. Godsey,-Jr., Serial No. 455,258, filed August 18, 19512, entitledPower measuring ,device for rotatingshafts which is closely related to'the present invention. Portions of the descriptive material appearing said copend- 'ing application have hereinbefore been included 75 '(see Fig. 2). The first mentioned expedient,

in this specification for the purpose of completeness. This application has been abandoned but reference may be made to United States Patent 2,461,685 which issued on February 15, 194.9, for the descriptive material hereinabove referred to.

As previously mentioned in reference to the inductor generator type of powermeasuring device, the shaft must be rotating before the device (can be calibrated. The same condition ordinarily obtains in the power measuring device disclosed in the above-mentional copending application. The present invention, While related in character to that of said copending application, is of a design that utilizes the torque characteristic only of the shaft to obtain a voltage indicative of the torque being transmitted. It is therefore possible to obtain a voltage indicative of the torque applied to the given shaft whether the shaft is rotating or stationary.

Broadly stated, the present invention is an electro-magnetic device including stationary electricalcoil means; the device being sensitive to the torque characteristic of the shaft in a 'manner to cause a voltage to appear in the electrical coil means indicative of the torque in the shaft.

Referring now to the drawings there is illustrated in Figures 1 and 2 a torque measuring device embodying the fundamental principles of this invention and the description relating to'these figures particularly as to its function will apply generally to all the modifications shown since there appears in all the figures a dual structure substantially of the character illustrated in Figs. 1 and 2 so that automatic compensation is provided for such undesirable effects as shaft temperature, bending of the shaft, end thrust of the shaft and shaft vibration. The manner in which this is accomplished will presently become clear.

Numeral l designates a shaft the torque loading of which is to be measured, numeral 3 indicates a rotor assembly, and numeral 5 indicates an annular stationary member which is concentrically positioned about the rotor assembly 3. The rotor assembly 3 comprises a pair of axially displaced torque rings 1 and 9 having axial extending finger portions la and 9a. These rings are made of magnetic material and are secured to rotate with the shaft on bushings of non-magnetic material II and I3 so that the circulating magnetic fiux will not include the shaft if the shaft is made of steel. In addition the rings are spaced a predetermined axial distance apart to include a known gauge length'of shaft therebetween. The fingers on each torque ring are equal in number and are positioned in interlocking relation so that each finger on each ring has a face portion of any one finger associated with one of said rings positioned in close proximity to a face portion of a corresponding finger associated with the other of said rings. Fig. 2 illustrates in exaggerated form a proportional positioning of the parts. In this manner airgaps M are formed between each of the confronting face portions. In order to prevent variations in the confronting face areas radial grooves 15 are provided in one of the confronting face portions thus providing a limited axial face length on one of the face portions associated with each air-gap, the other face portioncooperating therewith being of sufficient axial Theradial depth of one finger asradial depth of the finger cooperating therewith namely the provision of the radial grooves I 5, effectively maintains a substantially constant confronting face area when said rings are relatively axially displaced due to tension or compression loading of the shaft and. the second mentioned expedient effectively maintains a substantially constant face area when said fingers are radially displaced or tilted due to bending of the shaft thereby automatically compensating for end thrust and bending of the shaft. Circumferential distortions of the shaft circumferentially displace one ring relative to the other thus increasing or decreasing the air-gaps 14 between each of the "cooperating fingers.

The stationary member 5 is annular in shape and is concentrically positioned about the rotor assembly 3 so that each of the annular rings ll and -19 forming the axial extremities of the stationary member have their inner peripheries or bores positioned in close proximity to the peripheries of the torque rings '1 and '9 thus forming two circular air-gaps 2i and '23. A coil 25 is secured within the annular recess "of the stationary member formed by the annular rings l1 and I9 and for the purpose of illustrating one method of metering the voltage across the coil, the coil is shown connected as one leg in a conventional balanced Wheatstone bridge circuit 21, the bridge circuit being supplied from a suitable source of alternating current and adjusted to a balanced condition when the shaft is not loaded sothat a voltage will not appear across th terminalsof an indicating meter 29 connected across the bridge.

Upon suitable energization of the coil 25 a flow of alternating magnetic fiux is induced in the stationary member 5 and the rotor assembly 3 which is indicated as circulating in a clockwise direction by the dotted arrows as illustrative of an 'instantaneous condition. Specifically the magnetic circuit includes the stationary member 5,, air-gap 2|, the right torque ring 1, a finger portion thereof la, an air-gap l4, finger portion 9a, torque ring 9, air-gap 23 and back to the stationary member 5. The air-gaps 2| and "23 are preferably so adjusted that the magnetic reluctance appearing thereacross is small compared to that of the air-gaps 14. It may now therefore be seen that, whether rotating or stationary, if the shaft is not transmitting torque, the circulating alternating magnetic flux will maintain a substantially constant effective or instantaneous value and the voltage in the coil 25 will maintain a correspondingly constant value. If, however, there is circumferential deflection of the shaft due to torque the'air-gaps l4 formed bythe interlocking fingers la and So will increase or decrease depending upon the direction of the distortion to substantially proportionally change-the value of the circulating magnetic flux. Changes in the "value of the magnetic flux correspondingly change the value of the impedance of the coil .25 and therefore the voltage drop appearing across said coil, thereby unbalancing the bridge circuit of which it forms one leg and causing a voltage "to appear across the terminals of "the in- (heating meter '29 indicative of the circumferential-defiection or torque of the shaft.

From the foregoing disclosure it "may now be seen that a novel form of "magnetic strain gauge is provided in which the stationary member "comprises the coil and core assembly and the rotor assembly comprises the armature. The structure disclosed, however, has the distinct advantage of eliminating the necessity for slip rings and brushes for supplying the current to the coil;

Fig. 1. In these figures parts similar to those in Fig. 1 will be given like reference numerals.

Referring now to Figs. 3 and 4 it may be seen that the torque rings no longer have portions of each thereof positioned inclose proximity but are entirely separated and have a third ring 31, termed a reference ring, centrally disposed therebetween and secured to rotate with the shaft on a bushing 33 of non-magnetic material. 'In

this embodiment of the present invention the torque rings have been modified and, instead of having the finger portions "la. and 9a as in Fig. 1, are provided with radial teeth '8 and 10. Reference ring 3! is provided with axially extending fingers in each of its extremities which are disposed in interlocking relation with the radial teeth of the torque rings 1 and 9 such that face portions of the fingers are positioned in close proximity to face portions of the radial teeth as clearly illustrated in Fig. 4. This positioning of parts form the air-gaps 14a and [4b. Further the positioning of the parts forming the air-gaps 'Hla and Nb provides a construction which, upon circumferential distortion of the shaft, will increase one air gap while decreasing the other, that is, the faces :of the radial teeth of the torque rings confronting the fingers of the reference ring lie in the same axial plane, and the corresponding faces of the fingers lie in the same axial plane so that, upon circumferential distortion or twisting of the shaft and corresponding angular movement of the torque rings relative to the reference ring, the radial teeth of one torque ring will move away from the cooperating fingers of the reference ring and the -radial teeth of the other "torque ring will move closer to "the cooperating fingers of the reference ring, thus increasing one air gap while decreasing the other.

Stationary member "5 comprises the rings 11' and F9 corresponding to rings l'l and IQ of Fig) 1 and in like manner their inner peripheries or bores are positioned in close proximity'to the peripheries of the torque rings thus forming circular'air gaps 21 and 23. A thirdring'35 is dis-- posed centa'lly of rings l1 and i9 and has its inner periphery or bore positioned in close proximityto the peripheryof "the reference ring form-' ing a further circular air "gap 37. Axially disposed of the three rings and secured thereto on their peripheries are supporting bars 39 which serve to axially space and support the rings. Coils 25a, 25b, 25c and 25d are Wound abouteach of the bar portion-s between each of the rings. In this modification of the invention rings 40 of bearing material secured to the stationary member =5 in sliding contact with the peripheries of each of the torque rings are provided to maintain a 'fixedconcentric disposition of the stationary member-relative to the rotor assembly and further to prevent relative axial travel of either the stationary member or rotor assembly-thus preventing errors introduced by. radial displace-: ment of either'the rotor assembly or stationary:

member and effectively preventing changes; in confronting face areas due to relative axial shift of the parts forming air gaps 2|, 23 and 31. The bearings 40 may also be utilized, if -made.of suit.- able magnetic material, to complete the magnetic circuit thus either supplementing or eliminating the'air-gaps 2| and 23.v a

As, shown in the drawings, each pair of,,coi1s associated with each torque ring are connected in series circuit relation, that is, coils 25 uhand 25b are in series and coils 25c and 25d are in series, each pair in series being further connected to form one leg of a conventional bridge circuit. Upon suitable energization of the coils a magnetic flux linked with each coil may be induced to flow in the stationary member and. rotor assembly in the instantaneous directions indicated by the arrows and which at zero torque of the shaft may be adjusted, assuming the air-gap characteristics to be equal, by the potentiometer slider on the potentiometer 4|, each half of which-forms one leg of the bridge circuit, so thatthemagnetic induction across the air-gaps 2| and Ma, for example, associated with coils 25a and 25b will be equal and opposite to that appearing across air-gaps 23 and 14b.

Assuming now that torque is being transmitted in a clockwise direction from left to right of the shaft it will be seen that the air gaps formed between the confronting faces of the torque ring 9 and the reference ring 3! will be increased while those formed between the confronting faces of the torque ring 1 and the reference ring 3| will be decreased thus unbalancing the normal circulating magnetic flux associated with each coil to correspondingly increase the voltage across one pair of series coils while decreasing the voltage across the other pair of coils thus unbalancing the bridge circuit and causing a voltage to appear across the terminals of the indicating meter 29 connected across the bridge tomeasure unbalance therein. The voltage unbalance or difference between the coils being indicative of the circumferential distortion or torque applied to the shaft. l As an alternative, yet equally desirable form of the magnetic circuit described, the coils may be so energized as to induce flows of alternating magnetic flux in the stationary member and rotor assembly in such direction that they will oppose each other in the central ring 35 and for zero torque the total alternating magnetic flux in the central ring 35 preferably will be zero. Thus the magnetic circuit includes the bar 39, ring I1, air-gap 2|, the right torque ring 1, airgap Ma, reference ring 3|, air-gap 14b, left torque ring 9, air-gap 23, and the ring l9 connected to the bar 39. When the shaft transmits torque the air-gaps Ma and MI) formed between the torque rings and the reference ring. are changed, one increasing while the other decreases, thereby unbalancing the magnetic circuit and causing an alternating magnetic flux to appear across the air-gap 31 and flow through the central ring 35. An alternating magnetic flux linked with one pair of coils is therefore increased while the other is decreased which correspondingly changes the value of voltage across each pair of coils to cause a voltage difference to appear across the terminals of the indicating meter indicative of the torque being transmitted by the shaft. When the coils are connectedas described in thisparagraplnthe flux carrying elements of the torque-meter form in eifectamagnetic bridge. circuit.-

It may beseen from Fig. 3 that upon passing a. plane transversely'of the structure centrally thereof, two structures will be obtained essentially of the same character as that indicatedin Fig. 1,- hence the term dual structure. It may further. be .-seen that such undesirable effects as tilting of the torquerings relative to the reference ring due to shaft bending, which under some condi-. tions may, change the air gap characteristics, will have a like effect. upon the air-gaps; formed by eachof the torque rings; these variations will be of a balanced nature, and will have but little effectupon, the balance of the bridge and the indicator reading. Axial displacement of, the torque-rings relative to thereference ring due to end thrust will also have balanced effects upon; the'air gaps. In the same manner temperature effects and vibration effects are compensatedfor;

' Itis not to be construed from the descriptive disclosure hereinbefore made and the illustration of- Fig. 3 that the structure of Fig, 3 may function only as shown since, in some cases, it may be desirable to have two coils only, for example, 25a and 25c, In still another case it may be de sirable to increase the number of coils.

, Fig. 3 may be still further modified. as shown in Fig. 11, by providing, in place of the central ring 35, a ring 35a of substantially the samestructure as the torque rings 1- and 9, winding a-pick-up coil 63 about each of the radial tooth portions thereof and connecting the coils thus formed in either suitable series or parallel circuit relation, the ring 35a thus forming a core memher for the coils. The coils 25a and 250 will then be connected to a suitable source of alternating current and so energized as to induce a flow of alternating magnetic flux of such direction that the alternating magnetic fluxes associated with each of the coils 25a and 250 will oppose in the central ring 35a. as indicated by the arrows. The alternating magnetic flux thus induced will be ;so adjusted by adjusting the voltage of the coils that for zero torque the total alternating magnetic flux in the central ring will be substantially zero. Thus when the shaft transmitstorque flux will appear in the central ring by reason of the variations in the air gaps-Ma and Mb between the torque rings and the reference ring; and the unbalanced alternating magnetic flux across air-gap 31 will generate a voltage in the pick-up winding 43 on this central ring indicative of the torque transmitted by the shaft.

f The function of the modification of the inven-; tion shown in Figs. 5 and 6 is substantially the same as that of Fig. 3. Temperature, vibration, shaft bending and end thrust effects are all auto-v matically compensated for in a manner identicalwith the modification of Fig. 3. The design, ofv course, is much improved. By providing the. flanges 45, 4'8 and 4.9 onthe shaft and seating the elements of the rotor assembly thereon, 'circumferential distortion or deflection of the shaft surface onwhich the elements are secured is effectively avoided, the distortions of the shaft being largely restricted to the shaft lengths on either side of the flanges. This reduces the pos-jv sibility of the various rotor elements shifting on the shaft surface from their predetermined settings. Relative axial shift between the station: ary member and the rotor assembly, in this in stance, is effectively prevented by providing bearings secured to the stationary member and seated 9 th fl nge 45. an; h Server -r centrically' position the stationary member about .the' rotor -assembly and. lock the stationary membe: and. rotor assembly axially together. As may be seen from the drawings, the stationary member is'annular' in shape and is provided with lami- -nated rings Ma, 35?), and Illa which have their inner' bores positioned in close proximity to the peripheral surfaces of the rotor assembly. The

laminated ring construction provides electrical characteristics more favorable to the flow of an alternating magnetic flux; Circular coils 25c and 25 are located in the annular recesses formed in the stationary member by the rings Ila, 35b and [9a, eachcoil being connected in a bridge circuit as one leg thereof-such that unbalances invthe voltage across the coils due to torque of 'the shaft will unbalance the bridge circuit, which unbalance is measured by the meter 29.

- In many cases of shaft installations space limitations are such that it is impossible to-attach a'power or .torque measuring device about the shaft. In=installations of this type, where a hollow shaft may be utilized having one end thereof accessible, a reversed or'inside-out modification of the structure illustrated in Fig. 5 may be used. This adaptation of the invention is illustrated in Figs. 7 and 8. A hollow shaft la may be supplied with power through a spur gear 5t. The shaft installation is shown supported on'its' right end on a bearing race 53 seated on a housing 55, a fragmentary portion of which is shown. Rotor assembly 3a is positioned internally of the ,shaft, the torque rings and the reference ring being relatively disposed as previously described. The stationary member 5a comprises a tubular support 57, the rings [1, l9 andv 3'5 and the circular cells 256 and 25f positioned in the annular recesses between the rings. The coil leads are brought out through the tubu lar member and the coils are connected each as one leg in the conventional bridge circuit. Concentric positioning and axial locking of the stationary member relative to the rotor assembly is accomplished by means of the bearing supports 59 and GI and the stationary member is stationarily secured to the housing 55 or other convenient stationary support.

On large diameter shafts as, for example, marine propulsion shafts it often is not practical to build a torque measuring device to completely encircle the shaft. The modification illustrated in Figs. 9 and 10 adapted to measure the torque of this character of shaft is similar to that of Fig. 3 with the exception that the stationary member does not completely encircle the shaft and the rotor assembly is slightly modified to more practically suit the conditions. Two stationary members are here provided although one would be sufficient and more than two may be used if desirable. The coils a, 25b, 25c and 25d are here also arranged with each pair of coils associated with each torque ring connected in series circuit and each pair of coils forming one leg of a bridge circuit. The rotor assembly comprises the usual torque rings 1 and 9 and the reference ring 3| having fingers projecting therefrom positioned in close proximity in the manner previously described. Circular segments of the stationary member are concentrically positioned in close proximity to the peripheral torque ring and reference ring surfaces. The expedient of employing fewer fingers on the several rings, as previously mentioned, is but practical application since the device-will operate satisfactorily should there be but one air gap formed between each ring. A

'10 means for maintaining. accurate spacing between the stationary members and rotor assembly is illustrated in Fig. 12 in which a bearing surface of non-magnetic bearing material 62- is secured to the stationary member. This material is of predetermined thickness and permits the stationary members to follow the shaft motion which may result from vibration thus maintaining a predetermined spacing between the elements.

From the foregoing it is obviousthat applicant, with his novel form of torque measuring device, has provided means'for continuously indicating or measuring the" torque being transmitted by a shaft whether rotating or stationary- The inventive electromagnetic device, or more specifically, magnetic" strain gauge, operable in response to slight circumferential distortions of the shaft and serving as the shaft pickup element,

provides means for indicating shaft torque in. a degree of accuracy previously unobtainable. Furthermore, itwil'l be. seen upon inspection. of the various illustrations in the drawings that the torque measuring device will operate satisfactorily at high speeds of rotation by reason of its balanced construction. By utilizing magnetic air gaps for transmitting electrical energy to the rotating parts andproviding all electrical wind ings on the stationary member, the necessity for slip rings and brushes with their error introducing electrical characteristics is eliminated and, in addition, due t'o the highly sensitive yet stable operation of the device the need for relatively long gauge length of shafts for obtaining the necessary magnitudeof circumferential deflection is also eliminated;

The foregoing disclosure and the showings made in the drawings are merely illustrative of; the

principles of this invention and are notto be interpreted. a limiting sense. The onlylimitations are to be determined from the scope of the appended claims.

I claim as my invention:

1. Apparatus for indicating the torque of a shaft comprising, in combination, stationary electrical coil means, magnetic flux paths associated with said electrical coil means, means for producing an alternating magnetic flux in said magnetic flux paths, means included in each of said magnetic flux paths for varying the reluctances of said flux paths in response to the torque characteristics of said shaft for changing the value of said alternating magnetic flux to thus induce voltages in said stationary electric coil means indicative of the torque of said shaft.

2. In a device for indicating the torque of a shaft, comprising, in combination, stationary electric coil means; magnetic circuit means, including flux paths linking said electric coil means; means for producing an alternating magnetic flux in said magnetic flux paths; means, including a plurality of relatively displaceable elements included in each. of said magnetic flux paths variable in relative position of its elements in response to the torque of said shaft, for changing the value of said alternating magnetic flux, whereby voltages are induced in said stationary coil means indicative of the torque of said shaft.

3. In a magnetic device responsive to the torque of a shaft, the combination of, a pair of relatively displaceable members, at least one magnetic element supported by each of said members and each element having at leasta portion thereof 'disposedi in proximity to the other of said elements so that an air-gap is formed therebetween, stationary electromagnetic means congap, in dependence of the magnitude of the torque loading of said shaft.

4pm a magnetic device, the combination of, an elastic member of substantially circular sectionfat least two magnetizable elements, means non-magnetically securing said magnetizable elements at'axially displaced points along said elastic member, said m'agnetizable elements having portions of each thereof arranged in axial over- --lapping relation to form at least one small circumferential air-gap therebetween, the construc- 'tion'and arrangement providing for variation in the circumferential length of said air-gap upon rtor'sional deflection of the elastic member, and

stationary electromagnetic means constructed 'and arranged for magnetic flux linkage with said magnetizable elements and the air-gap therebetween.

5. Apparatus responsive to the torque of a shaft comprising, in combination, stationary electrical -coil means, a magnetic circuit linking said stationary electrical coil means, said magnetic circuit including relatively displaceable magnetic elements disposed to form at least one air-gap therebetween, means for supplying alternating current to said stationary electrical coil to induce "prising, in combination, a single stationary electromagnetic unit including electrical coil'means,

'a magnetic flux path associated with said stationary electromagnetic unit including at least one air gap, means for producing a magnetic flux in said magnetic flux path, means responsive to operating characteristics of said shaft independent of the rotation of said shaft for varying the magnitude of said air gap thereby varying the flux linkages with said electrical coil means and inducing a voltage therein indicative of operating characteristics of said shaft.

' 7.111 combination, a stationary electromagnetic means, a torque receiving element positioned in close proximity thereto, a magnetic flux path including said electromagnetic means associated with said torque receiving element, means for producing a magnetic flux in said magnetic flux path, changes in the value of said magnetic flux correspondingly changing the voltage in said electromagnetic means, relatively movable elements associated with said torque receiving element and included in said magnetic flux path for changing the value of said magnetic flux in dependence of deflections of said torque receiving element when subjected to torque,'and means for measuring the voltage in said electromagnetic means whereby the relative movement REFERENCES CITED The following references are of record in the file of this patent:

FOREIGN PATENTS Country Date Number Great Britain 1910 

